Clones - Sir Joseph Williamson

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Plant Clones
• To a biologist, a clone is a population of
genetically identical organisms.
• Clones are produced naturally when organisms
reproduce asexually.
• This happens commonly in bacteria, fungi,
insects and plants.
• Mitotic cell division, or binary fission in the case
of some microbes, ensures that the same genetic
information is passed to the offspring.
To a biotechnologist:
A clone is an exact copy of:
 DNA
 A gene
 A chromosome (or genetic material)
 A cell
 The whole organism
You will need to differentiate between reproductive
and non-reproductive cloning.
Reproductive cloning:
 Produces a whole
organism
 Normal with:
 Natural cloning
 Artificial propagation in
plants
 Artificial embryo splitting
 Somatic cell nuclear
transfer in animals
Non-reproductive cloning
(aka therapeutic cloning):
 Produces cells or
tissues to treat:
 Genetic disorders
 Degenerative conditions
 Damage caused by
trauma
Plant Clones
• Producing plant clones is relatively easy:
– Many plants reproduce asexually and so produce clones
naturally
– Cuttings often ‘take’ easily, i.e. produce roots and grow
– Humans have made use of this for many thousands of
years
• Some of the micropropagation techniques used to
artificially produce clones are extensions of these
simple techniques.
• Others depend upon manipulating conditions so
that cells initially just grow, and then are persuaded
to differentiate.
Plant cloning
• There are many examples of natural
vegetative propagation in plants producing
clones. These include bulbs and corms, tubers,
runners, rhizomes and root suckers.
Asexual reproduction in plants
• A rhizome is a modified stem serving as an organ of vegetative
reproduction e.g. Aloe vera
• Adventitious buds develop into above ground stems and leaves,
forming on roots near the ground surface and on damaged stems (as
on the stumps of cut trees).
•A form of budding called suckering is the reproduction or
regeneration of a plant by shoots that arise from an existing root
system. Species that characteristically produce suckers include Elm,
Dandelion, Yew and members of the Rose Family.
Another type of vegetative reproduction is the production
of bulbs.
Plants like onion and tulips reproduce by forming bulbs.
Other plants like potatoes reproduce by a similar method of
producing tubers.
Aerial stems, called runners or stolons are important
vegetative reproduction organs in some species e.g.
strawberry, numerous grasses and spider plants.
Runners (stolons)
Q. What are the advantages and
disadvantages of such vegetative
propagation (cloning)?
• Consider uniformity;
• ability to colonise an area and exclude competitors;
• ability to withstand destruction of above ground
foliage (by insects, grazers, fire or human activity)
• fallback position if sexual reproduction fails
• persistence and ability to spread (if a weed)
• lack of genetic variation
• speed of spread or colonisation of a new area
(compared to sexual reproduction and seed dispersal).
Advantages
• Uniformity
– It is likely that it is suited to the area that it is growing
in, so all new plants will be equally suited.
• Ability to colonise an area and exclude
competitors
– Suited to conditions and dense growth
• Able to withstand destruction of above ground
foliage
– By insects, grazers, fire or human activity
– Regenerate from underground parts
• Fallback position if sexual reproduction fails
Disadvantages
• Uniformity / lack of genetic variation
– If conditions change and no longer suited...
• Persistence and ability to spread
– If it is a weed, it is a disadvantage to the farmer
(but an advantage to the weed)
• Rapid spread and colonisation of a new areas
– Compared to sexual reproduction / seed dispersal
Plant Clones
• Producing plant clones is relatively easy:
– Many plants reproduce asexually and so produce clones
naturally
– Cuttings often ‘take’ easily, i.e. produce roots and grow
– Humans have made use of this for many thousands of
years
• Some of the micropropagation techniques used to
artificially produce clones are extensions of these
simple techniques.
• Others depend upon manipulating conditions so that
cells initially just grow, and then are persuaded to
differentiate.
Natural Clones in Plants
• There are many examples of natural
vegetative propagation in plants producing
clones.
• These include:
– Bulbs and corms
– Tubers
– Runners
– Rhizomes
– Root suckers
Bulbs and Corms
• Bulbs are condensed
shoots which store food
reserves in swollen or
fleshy leaf bases
– e.g. onions and daffodils
• Corms store food reserves
in swollen stems
– e.g. crocus and gladiolus
Shallot (a member of the onion
family)
A single bulb makes many new bulbs.
• In either case, lateral buds
can develop and grow
into new plants.
Stem Tubers
• In the potato, lateral
buds grow outwards
from the stem and
then down.
• The stem swells as
food reserves are laid
down.
Potato tubers
The eyes of a seed potato produce the
shoots and roots. Swelling appear at
the end of side shoots or stolons.
– This only happens at
the tip of the shoot,
rather than along its
length (as happens with
rhizomes).
Runner
• A runner is a specialised
stem that grows away
from the parent plant.
• Where a node touches
the ground:
– Roots appear
– The bud at the node
grows
– A new plant is produced
Strawberry runner
Adventitious roots form so the
plantlet can obtain water and
mineral nutrients and become
independent of the parent plant.
• Whilst growing, the new
plant gets its nutrition
from the parent to which
it is still attached via the
runner.
Rhizome
• A rhizome is a specialised
underground stem that
grows horizontally.
• The old part of the stem
does not die.
– It can last for many years.
– It is swollen with food
reserves.
Couch grass
Underground stems grow from the
main plant, allowing it to produce a
dense patch and allow the plant to
spread.
• The growing tip turns up
and produces leaves and
flowers.
Sucker
• Meristematic tissue in the
root grows and produces
basal sprouts.
• Basal sprouts can be:
– Close to the parent plant
• Produces a dense patch of
plants
– Some distance away
• Allows colony to spread
Raspberry
Meristematic tissue in the root
produces sprouts which allow it to
establish in a patch and spread to new
areas.
• The example of English
elm (Ulmus procera) will
be considered in more
detail later.

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